WordPress.org

Installing The Plugin

Extract all files from the ZIP file and then upload it to /wp-content/plugins/.

Open up your browser and type in the URL to your admin area and then "plugins.php", like this:

http://yoursite.com/path/to/wordpress/wp-admin/plugins.php

Scroll down and activate the plugin. It'll fix your error and then automatically deactivate.

See Also: "Installing Plugins" article on the WP Codex